*
    margin 0
    padding 0

.header 
    height 100px
    background-color green
    h1 
        font-weight 700
        font-size 26
        color blue

.footer
    background-color pink
    height 100px

main  
    display flex
    nav,div,aside
        // float left
        // display inline-block
        height 500px
        width 200px
        background-color yellow
    nav
        background-color grey
    aside
        background-color red
    div
        //flex 1    div占据剩余的位置
        width calc(100% - 400px)
